The present invention relates to cutting inserts of the type that are referred to as disposable cutting inserts or indexable cutting inserts and which are adapted to be detachably mounted on a tool holder for mounting in a machine tool for cutting operations, primarily turning operations. More particularly still, the present invention is concerned with the formation of the cutting edge land area and the chip controlling groove in a circular cutting insert. Such cutting inserts are usually made of coated or uncoated cemented carbide but different ceramic hard materials are also feasible.
A round cutting insert can often cope with a large variety of profiling operations ranging from finishing to roughing. Their round relief surface is usually of a frustoconical shape in order to allow for sufficient clearance. Because of this clearance, they are normally single-sided. They have a wide capability in chip control and are allrounders that generate a good surface texture even at high feed rates. However, they also entail some drawbacks, such as the fact that it is not possible to choose a particular entering angle at a particular cutting depth. Furthermore, it is not possible to select an appropriate entering angle as a function of the feed. This of course is due to the fact that round inserts have a basically uniform cutting geometry around the whole circular cutting edge. As examples of such cutting inserts, reference is made to U.S. Pat. No. 4,606,678.
In U.S. Pat. No. 3,383,748 a round cutting insert is disclosed with a circumferential chip-breaking groove along the circular cutting edge. This groove may have a varying width and depth and is stated to produce chip control at light chip loads as well as at heavy chip loads by orienting the groove in the appropriate position with respect to the active portion of the cutting edge. However, this cutting insert causes swarfing problems in general and does not work satisfactorily, particularly at small cutting depths, because the chips are not broken properly.
Further, DD-C-264 391 discloses a round cutting insert which comprises six planar chip surfaces around the circular cutting edge. However, in practice, this cutting insert does not work properly because the planar chip surfaces do not manage to break the chips, which rather pass over the step-like shoulder unbroken. Further, the center island extends at six points practically to the very cutting edge, which is impractical because these extending portions become fragile and easily broken.